1. Field of the Invention
The present invention relates to a screw type extruding or kneading machine and a screw used therein.
Note, in this specification, including the claims, the term "an extruding machine" indicates any machine in which a material to be worked is moved by means of a screw revolving in a barrel, and includes, for example, a so-called "extruder" and an injection molding machine. The application of the extruding and kneading machines mentioned herein is not limited to the working of special materials but may be used for working plastics, ceramics, metalparticles, composite materials comprising polymers and inorganic fibers and/or inorganic powders, and any other material. In particular, they are suitable for working a hard material or a material containing a hard material.
2. Description of the Related Art
Various types of extruding and injection molding machines are used in the processes for melt spinning synthetic fibers and shaping synthetic resins. In this connection, new materials and composite materials have been developed and are in practical use. These are made by mixing hard fibrous materials such as glass fibers, metal fibers, inorganic fibers, carbon fibers, or other fibers, with a polymeric material during the mixing (prior to spinning or molding) of a pigment, stabilizer, or titanium oxide, etc., or during the premixing or shaping of resin composite materials.
Heretofore, all machines used for such mixing, extruding, pressing, shaping, and the like, have been made of steel. To improve the abrasion resistance and chemical resistance of these machines, improvements in the hardness of the steel surface by, e.g., alloying, plating, and fusion bonding of different metals, have been proposed, and some of these improvements are in practical use.
As the functions of the above-mentioned composite materials are improved, the heat resistances of the polymeric materials become higher and strength imparting components to be mixed become even harder. In such situations, the hardness of the metals of the above working machines can provide only a limited, usually insufficient, abrasion resistance. As a result, machine parts must often be renewed at very short intervals, which causes problems such as cost increases, reduced productivity, and destabilized molding conditions (for example, extruded products are remarkably varied between start-up and shut-down of machines, due to this remarkable abrasion) and the thus-necessitated exchanges of equipment.
Another problem is an incorporation of a metal into a working material, caused by the abrasion of the working machine. This is a particular problem when working recent super high pure materials.